It is known that mercaptans can be produced by the reaction of hydrogen sulfide and an olefin in the presence of a catalyst. For example, ethyl mercaptan can be prepared by reaction of pure ethylene and hydrogen sulfide without creating a problem for separation because the desired mercaptan is the only mercaptan product. However, where the reaction mixture comprises more than one olefin such as ethylene and propylene, it is likely to produce both ethyl mercaptan and propyl mercaptans resulting in separation difficulty because these mercaptans cannot be easily separated by a conventional, economics separation means such as, for example, distillation, extraction, filtration, and membrane diffusion. Therefore, it is highly desirable to develop a process for selectively producing ethyl mercaptan from a feed stream comprising, among others, ethylene and propylene.